The present invention relates to the field of suspension bump stop devices used in particular in motor vehicles in the suspension struts of the steered wheels.
The invention relates more specifically to a suspension bump stop device comprising an upper ring and a lower ring between which rolling elements, for example balls or rollers, are positioned. The upper and lower rings are generally mounted in contact with lower and upper bearing or support pieces, such as caps or cups. The upper and lower support cups form a housing for the rings of the rolling bearing and provide the interface between the said rings and the surrounding elements.
A suspension bump stop is positioned in the upper part of the suspension strut between the vehicle bodyshell and a suspension spring. The spring is installed around the piston rod of a shock absorber the end of which is connected to the vehicle bodyshell via an elastic block that filters out vibrations. The suspension spring bears axially, either directly or indirectly, on the lower cup. The upper cup for its part is fixed relative to the vehicle bodyshell.
The suspension bump stop allows axial force to be transmitted between the suspension spring and the vehicle bodyshell while at the same time allowing a rotational movement between the lower cup and the filtering elastic block. This relative angular movement results from a turning of the steered wheels of the vehicle and/or from the compression of the suspension spring. The upper and lower cups are able adequately to transmit axial load between the raceways and the cups. They have bearing surfaces that provide good load distribution. Means incorporated into the said cups may also provide axial retention of the various elements of the suspension bump stop and provide means of sealing.
In numerous motor vehicle strut devices, the seat on which the suspension spring bears via its lower end, on the opposite side to the suspension bump stop, is inclined with respect to the axis so that the line of force applied by the spring to the lower cup of the suspension bump stop makes an angle with respect to the axis of the shock absorber. One example of a device of this type is illustrated in patent application FR 2 783 204.
This results in radial forces applied by the spring to the lower cup of the suspension bump stop. These radial forces may cause the lower cup to shift slightly in a radial direction with respect to the upper cup.
Now, the sealing of the bump stop between the two cups is often afforded by soft sealing lips which bear against rubbing bearing surfaces. Because the suspension bump is under the bodywork of the vehicle, near the wheel, it is particularly exposed to being splashed with water. It is therefore necessary for the sealing to be particularly effective.
Patent application FR-A-2 857 906 recommends embedding a metal reinforcing insert in the lower cup. However, the suspension bump stop of that document has the disadvantage of providing only a simple narrow passage between an upper cap and the lower support cap that supports the rolling bearing in order to seal the bump stop.
As a result, under certain conditions, for example when the vehicle is driving along a flooded road surface or alternatively when the vehicle is being cleaned with a high-pressure jet wash, there may be some ingress of water into the rolling bearing with detrimental effects on bearing life.
In addition, in the event of eccentricity of loading as in a device as illustrated by patent application FR 2 783 204 mentioned hereinabove, the sealing means provided on the cups are liable no longer to come into contact with their bearing surface, at least in certain regions, thus reducing the sealing.
It might be possible to increase the radial geometric interference between the lips and their bearing surfaces in order to overcome this problem but that would have the disadvantage of excessively increasing the frictional torque of the bump stop.